1. Field of the Invention
The invention relates to a supercharged pressure control system for internal combustion engines with turbochargers and in particular, to a control system which enables proper control over the supercharged pressure in the presence of variations, in the operating conditions such as flow response, from engine to engine or from turbocharger to turbocharger, which includes a supercharged pressure regulator means.
2. The Related Art
It is generally recognized that a turbocharger enables a torque produced to be increased over a range from a low to a high speed by providing a variable capacity of a turbine. An example of a variable geometry turbocharger is disclosed in Japanese Publication of Unexamined Utility Model Application No. 50,310/1978 and Japanese Publication of Unexamined patent Application No. 176,417/1983. In these variable geometry turbochargers, a flap valve or swing valve is disposed in the inlet to a turbine and is controlled in accordance with a load on and the number of revolutions of an engine to define a variable geometry nozzle. In this manner, the flow rate of an exhaust gas supplied to the turbine is varied to provide a variable capacity thereof to thereby establish a high supercharged pressure over an extended interval in order to provide an increased torque output.
Specifically, the opening of the nozzle is controlled over the entire range of operation by a function generator which responds to signals representing a load on and the number of revolutions of the engine. Accordingly, if there are variations in the flow response from engine to engine, in the turbocharger response or in the operational responses of components of the control system, a supercharged pressure which is actually established will deviate from a target value and may overshoot, causing damages to the engine. To accommodate for this, it is a usual practice to provide a certain margin for these variations when establishing a supercharged pressure which does not result in damages to the engine. However, this detracts from providing an improvement in the output.
As an alternative, an arrangement employing a movable ring nozzle is also known in which the opening of the nozzle is detected and used in a feedback control to achieve a target opening, thereby preventing any variation in the supercharged pressure which may result from variations in the response. However, a specific manner of feedback control is only illustrated by the use of a potentiometer, and a fully effective arrangement is not disclosed.
Therefore, further development is still required to maintain flow flexibility and pressure variability throughout operation.